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Royer induction heater

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Kizmo

Wed Mar 21 2012, 10:54AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Yes those eurofarads are oil immersed metallized polypropyleme film-foil hybrids just like cde942 series. I have 60kHz drsstc with eurofarad mmc and its perfect :)

Linas

Sat Mar 24 2012, 08:57AM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

ok, i get 4 of them, so 15uF and 2uH should give me around 29KHz
question is, what kind of driver to use ?
i am thinking about PLL, or maybe i should use phase prediction with inductor ?
I will use SKM400GB125D in final version and for testing SKM200GB125D

Gabriel35

Sat Mar 24 2012, 02:13PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Nice stuff out there!

Gabriel35

Thu Mar 29 2012, 08:23PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Linas, I Think that the PLL is the best choice for you...
Use KimLadha's, Uzzor's or Iam ones...

I'm thinking about that too...

Good luck!

Hey Marko! How's your progress on the royer?
What about the bigger supply and caps that you said you will test?

Let's make a Royer-Melting-A-Screw challenge!
The more I work with Royer, more I get conformed that It will only melt chapes of steel that have a good copling to the workcoil like you said, and that's not the screw characteristic.
Good for melting coins and pieces of aluminum, but would it be capable of turning a screw or nail in hot liquid? (The problem is that when it needs the power (curie point is achieved) it drops down, because the resonance of the circuit changes and it don't have feedback to keep mosfets switching at tank's exact frequency).

What do you guys think?

Marko

Thu Mar 29 2012, 09:21PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hello

Well, I blew up the original circuit by accidentally soldering a power supply wire into a wrong place. I have a big transformer I made from some scrap E cores, but it's heavy and buzes like hell - and I'm not sure if it'll even be necessary for this little handheld circuit. It's being refitted now with a cooling fan and a handle with a switch so it can be used conveniently for longer times without having the caps overheat.

I did start making an entirely water cooled MMC with caps submerged in water,but gave up on that since RogerinOhio sent me two of those monster eurofarad 100uF 500A caps which I think beat pretty much any MMC I can make.

I made a several attempts with BJT's thinking I might have some luck, but always ended up with the circuit displaying bizzare behavior and eventually blowing up. It doesn't seem like this circuit is achievable with low gain devices.

I returned to studying mosfets and igbt's and decided to find a way to bias them properly so they don't blow up instantly after the power supply is turned on.

I also intend on replacing diode feedback with capacitive or inductive feedback.

Providing stable bias to devices that display severe nagetive tempco proved a big problem.
Firstly I tried using drain resistors in attempt to stabilize them, but this apparently reduced gain and compromised the oscillation in a similar way bjt's did.

I settled on using 5 series 1N4007's as a temperature sensor, bolted onto one mosfet with heat goop. I used their voltage drop to bias the mosfets directly; and after some fiddling I got both feedback methods working!

The circuit as always displays lots of parasitic oscillations which will have to be silenced by copious amounts of ferrite beads (this seems to work so far, though beads get very hot).

I hope to try scaling this up to a mains powered circuit, hopefully without it blowing up this time!

Cheers,

Marko

Gabriel35

Fri Mar 30 2012, 02:35AM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Can't wait to see Royer oscillator running right from the mains!

I've been working with the royer too.

Now I got a serious Tank that is water cooled, with a radiator, and a bank of 32x 110nF 1200v capacitors that get just a little bit warm when operating.

The hell is that ALWAYS when i'm running the circuit something pop, the mosfets or the rectifier bridge...(the rest of the circuit keeps perfectly)
(I'm using 13v zenners instead of 12v ones for IRFP260N's.)

I found on the hard way that, for some reason when the ammeter displays more than 35A of AC current on the transformers side, the mosfets die cold seconds before measuring that current. (I'm using pretty large heatsinks with cooler on them.)

I think that it's because the reactive current of the whole circuit is getting within it's limits (something near 50A) and the mosfets can't handle this. (This is the bad thing about large currents and low voltage)
That is the main advantage of using more voltage to the royer circuit.(Like rectified mains perhaps)

I was running it one minute ago and my rectifier popped, It was a KBPC3510 (35A 1000v) (Measuring 31A on AC side)
Misterious failure (Maybe system latched up?)
What bridge rectifier do you use Marko? With heatsink?

I've found that if I try to run the circuit with 39v (Yes it sags on 39v) and with more than 3,8uF of capacitance on the tank, the circuit become more prone to failure (when I put something big on the work coil, and this object hits curie temperature, the current starts to rise and the mosfets burn...

Now I'm using exaclty 3,48uF and I think it is still so much for the circuit to handle with 39vDC...

Pretty nice Eurofarads! Can't wait to see some photos or them working!

Lets keep the progress and see if we can get a way of making the old and good Royer to run from mains!

What do you think about that misterious failures and things like that? I'm getting my money out of my walet just buying mosfets and bridges...

Cheers!

Forty

Fri Mar 30 2012, 03:57PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

Well I don't know much about induction heaters because I haven't gotten around to building one yet, but could the ripple voltage from rectifying that kind of current be causing a problem with the fets or at least some instability somewhere?

Gabriel35

Fri Mar 30 2012, 05:14PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

I doubt... I'm using 8x 470uF 400v Electrolytics to filter the voltage... This results in 3750uF...
Do you think I need more smoothing? how Can I do that properly?

Forty

Fri Mar 30 2012, 10:29PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

So you've got about 2.2v of ripple per amp that you're drawing on the rectified side. (

and

)

That could be pretty significant if you've got components that care about the ripple. But again, I'm not really sure if it affects the mosfets.

Gabriel35

Fri Mar 30 2012, 11:07PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

what is the better way to get rid of the ripple? DO you guys think that this ripple can be bad for the circuit?

Adding more capacitors ar a inductor? what do you think?

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